Various arrangements and systems are known for measuring the filling level, in particular, in fuel vessels. For example, in the case of capacitive filling level sensors such as are known from U.S. Pat. No. 2,700,901, a rod-shaped capacitor is dipped vertically into the fluid. The fluid and the gas located above it act as dielectrics with different dielectric constants of this capacitor. When the filling level changes, the capacitance of the capacitor also changes, and it is consequently used as a measurement variable for the filling level in the vessel.
By means of various influences, such as fabrication tolerances, long-term change and the change in the composition of the fluid in the vessel, the characteristic curve of such a filling level sensor changes. In addition, after manufacture, adjustment is necessary in order to compensate for tolerances. A large number of fluids also separate out when standing over a relatively long period or they combine with other substances such as water, and thus change their physical properties, including their dielectric constants, independently.
For these reasons, when capacitive sensors which operate continuously are used, measuring errors occur, since, in addition to the filling level, the height-dependent dielectric constants also affect the filling level measurement in a nondeterministic way.
In order to avoid these disadvantages, discretely operating filling level sensors have been disclosed. Such capacitively operating sensors have a large number of individual capacitors distributed over the entire measured height. The greater the number of measurement points, the greater the resolution of the sensor. This arrangement is independent of changes in the dielectric constant of the fluid and is thus immune to the abovementioned sources of error. Unfortunately, it is extremely complex and expensive. In addition, the resolution which can be achieved with such sensors is often too low, which is a further disadvantage particularly in situations where there are small filling levels.
The object of the present invention is to specify a filling level sensor which can be manufactured cost-effectively and simply, which operates precisely and without maintenance and which is largely independent of changes in the dielectric constant of the filling material.